During the next five years, we will continue to study epidermis and epidermal appendages in health and disease by focusing on keratin gene expression in a number of model systems. During this period, we shall use guinea pig epidermis, mouse hair root cells, cell lines such as ME 180 derived from pathologic human tissue and human epidermal biopsies to identify and characterize the keratin genes and to prepare radiolabelled probes of the study of gene expression. Probes will be used to analyze a number of physiologic states, such as mitosis and aging, a number of pathologic conditions, such as tumors, psoriasis and the several ichthyoses, and a group of pharmacologic agents, such as Vitamin A and corticosteroids. Ultimately, we will use the clones and probes developed to determine the nucleotide sequences of keratin cDNA, and the amino acid sequences of keratin in normal and disease states. In parallel, we will investigate the glycosylation and phosphorylation of keratin and other intermediate filament proteins in the models we have noted. We will use these data to identify and localize subunits of keratins in cells and tissue from normal and pathologic epidermis. The molecular biologic and biochemical evidence developed during these investigations should lead to a definition of the function of keratin and other intermediate filament proteins and to data concerning the relationships among keratin and other cellular constituents.